Authorization Bypass Through User-Controlled Key Affecting mcp package, versions <0.23.0
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Start learning- Snyk IDSNYK-RUBY-MCP-18017728
- published19 Jul 2026
- disclosed17 Jul 2026
- creditSrikanth Ramu
Introduced: 17 Jul 2026
New CVE NOT AVAILABLE CWE-639 (opens in a new tab)How to fix?
Upgrade mcp to version 0.23.0 or higher.
Overview
mcp is a The official Ruby SDK for Model Context Protocol servers and clients
Affected versions of this package are vulnerable to Authorization Bypass Through User-Controlled Key in lib/mcp/server/transports/streamable_http_transport.rb, which processes tool execution requests to /messages/{session_id} without verifying that the requester owns the identified session. An attacker who obtains a valid session ID can execute unauthorized tool calls and modify state on a victim's session by sending POST requests to /messages/{session_id}, with the tool responses delivered to the victim's SSE stream. Exploitation requires the attacker to obtain a valid session ID out-of-band, such as through network observation or logs.